In vitro test systems

Corona.iy Hea.rt Disea.se, A theory for atherogenesis (120) has been developed whereby oxidation of low density Hpoprotein (LDL) within the arterial wall is the critical first step. It has been hypothesized that sufficient intake of antioxidants would prevent oxidation of LDL and reduce development of coronary heart disease (122). Interest in determining the role of antioxidants in blocking LDL oxidation has led to the development of in vitro test systems. 

Sodium chlorite is not Hsted by the USEPA or any regulatory authority as a carcinogen. Studies conducted ia mice and rats did not show an increase in tumors in animals exposed to sodium chlorite in thek drinking water. Sodium chlorite has been found to have mutagenic activity in some in vitro test systems such as the Ames Salmonella reverse mutation assay without the presence of metaboHc activators. The significance of these test results in regard to human health is not clear because of the oxidizing effects of the chlorite ion (149). 

EFFECTS ON LABORATORY MAMMALS AND IN VITRO TEST SYSTEMS... 

Mayr U, Butsch A and Schneider S. 1992. Validation of two in vitro test systems for estrogenic activities with zearalenone, phytoestrogens and cereal extracts. Toxicology 74 135-149. 

The overall evidence indicates that endosulfan administered in vivo may be disruptive of reproductive hormone levels in male animals. On the other hand, endosulfan is neither estrogenic nor disruptive of thyroid or pituitary hormone levels in females in vivo, despite its weak estrogenicity in several in vitro test systems. 

H. Wagner, K. Kostka, C. Lehr, and U.F. Schaefer, pH profiles in human skin influence of two in vitro test systems for drug delivery testing. Eur. J. Pharmaceutics Biopharmaceutics 55, 57-65 (2003). 

Paper mill whitewaters and effluents are rich in bisphenol A (BPA), which is used in great quantities for the production of epoxy resins and polycarbonate plastics. Its presence in effluents has been reported as a result of its use in the manufacture of thermal paper or due to migration from plastic containers at the high water temperatures of whitewaters [35]. This compound is preferably analysed by GC-MS. The levels encountered in paper mill effluents are between 28 and 72 pg/L [36,37]. Another study revealed levels up to 226 pg/L [33]. Special in vitro test systems and animal experiments have demonstrated a weak oestrogenicity for BPA. Since aquatic wildlife could be endangered by paper mill waste discharges at the concentration that BPA is found, its survey in paper mill effluents should be taken into consideration. 

Parry, J.M., Arlett, C.F. and Ashby, J. (1985). An overview of the results of the in vivo and in vitro test systems used to assay the genotoxicity of BZD, DAT, DAB and CDA in the second UKEMS study. In Comparative Genetic Toxicology The Second UKEMS Collaborative Study, (Parry, J.M. and Arlett, C.F., Eds.). Macmillan, London, pp. 597-616. 

The entire safety assessment process that supports new product research and development is a multistage effort in which none of the individual steps is overwhelmingly complex, but for which the integration of the whole process involves fitting together a large and complex pattern of pieces. This paper proposes an approach in which integration of in vitro test systems calls for a modification of... 

At the same time, progress and critical examination over the last 15 years has led to the formulation of an equally impressive list of reasons for pursuing the development of in vitro test systems ... 

While there are no generally accepted in vitro test systems immediately available to completely replace all (or, indeed, any) of the regulatorily mandated in vivo testing requirements, there are test systems that can replace distinct components in vivo tests (or, just as important, preclude their having to be performed by providing information quickly that makes difficult go/no go decisions viable at an earlier (and cheaper) stage of development. 

H. Wagner, K. H. Kostka, C. M. Lehr, and U. F. Schaefer. Drug distribution in human skin using two different in vitro test systems Comparison with in vivo data. Pharm. Res. 17 1475-1481 (2000). 

Tukker JJ (2002) Characterization of transport over epithelial barriers. In Lehr CM (Ed) Cell Culture Models of Biological Barriers. In-vitro Test Systems for Drug Absorption and Delivery. Taylor and Francis, London, pp 52-61. 

Studies in the last few years in the fields of genomics and proteomics have made available to us an unprecedented number of targets with which to search for new drug candidates. While knowledge of a particular gene sequence, for example, may not directly point to a specific disease when the sequences are first determined, investigations of their presence in normal and diseased tissues could well lead to a quantitative in vitro test system that is not available today. The same can be said for the field of proteomics, but final decisions on the value of these new technologies cannot be made for some years to come. 

The in vitro approaches may give qualitative and under special circumstances, also, quantitative information. Information from in vitro experiments, in particular data on in vitro metabolism, has been used in PBTK models (Section 4.3.6). The use of data derived from in vitro test systems should be very carefully considered in the risk assessment until such approaches have been appropriately validated. 

Small-scale in vitro test systems may now be employed to assess biopharmaceutical properties or the drug s potential behaviour after in vivo administration. For example, drug penetration through monolayers of epithelial cells in tissue culture can be used to examine bioavailability. The drug s metabolism can be studied in vitro using hepatic microsomes and potentially toxic metabolites identified before problems arise in vivo Although not absolute, these tests... 

From our laboratory cultures of ]P. brevis, we are able to purify to homogeneity and crystallinity two toxins, namely T17 and T34(, ). Both toxins have been subjected to a variety of in vivo and in vitro test systems in order to ascribe specific actions to each(10-13). 

Comparative Toxicokinetics. There are no data on metabolism of hexachlorobutadiene in humans. On the other hand, toxic metabolites and proposed mechanism of renal toxicity have been evaluated in animals employing both in wVoand in vitro test systems (Dekant et al. 1990b Schneumann et al. 1987). It is not known if similar metabolic pathways and metabolites occur in humans. 

An extensive variety of in vitro test systems are available that can be used in supplementary investigational studies of the reproductive system. Examples of these systems include the maintenance of whole organs (e.g., isolated perfused testis/ovary), primary culture of gonadal cells and subcellular fractions of organs and cells. In vitro fertilization techniques have also started to show promise in evaluating functional end-points for toxic effects. The information obtained from such test systems can be invaluable in identifying potential mechanisms of action... 

In vitro testing systems are most useful in two important areas. First, they are useful in screening for toxicity, particularly in cases where sufficient in vivo data exist to validate the in vitro results. Second, in vitro tests are useful to study mechanisms of toxicity, and frequently they represent the only available approach for such studies. The wide variety of in vitro systems available to the reproductive toxicologist has been reviewed extensively (e.g., ECETOC, 1989 Chapin Heindel, 1993 Heindel Chapin, 1993 OECD, 1996b Genschow et al., 2000). 

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